Background: Ventricular tachycardia/fibrillation (VT/VF) associated with acute myocardial ischemia is the most common cause of sudden cardiac death, but its underlying mechanisms are incompletely understood. It is hypothesized that late Na+current (INa) contributes to arrhythmogenic activity in ischemic myocardium.Methods and Results:Langendorff-perfused rabbit hearts with regional ischemia in ventricles were optically mapped. Perfusion with ranolazine (10 μmol/L), a selective inhibitor of lateINa, significantly reduced excitation frequency and facilitated termination of VT/VF induced after occlusion of the left main coronary trunk. The activation pattern during ischemic VT/VF was characterized by breakthrough-type excitations (BEs) from multiple origins, predominantly in the ischemic border zone (BZ) and occasional short-lived rotors. Ranolazine perfusion significantly reduced the incidence of BEs in the BZ. Rotors tended to decrease with progression of ischemia and disappeared after ranolazine perfusion. During constant pacing, ranolazine attenuated ischemia-induced shortening of action potentials in the BZ without affecting conduction velocity, probably due toIKrinhibition. In intact hearts without coronary occlusion, ranolazine (10 μmol/L) terminated aconitine-induced VT by inhibiting focal arrhythmogenic activity in the injection site.
Conclusions: LateINa-mediated focal arrhythmogenic activity plays important roles in the maintenance of ischemic VT/VF in isolated rabbit hearts. Suppression of lateINaby ranolazine may be a promising therapeutic strategy to reduce arrhythmic death during the acute phase of myocardial infarction.
Keywords: Action potential; Ischemic ventricular arrhythmia; Late INa; Optical mapping; Ranolazine.